1. Field of the Invention
The present invention is a cut-off die comprised of a pair of fixed die halves separated from each other, with each fixed die half having an associating movable die insert so that openings of variable width are formed between stationary halves provided on the fixed die halves and movable halves provided on their associating movable die inserts. The widths of the openings are decreased in response to cam means provided on a cut-off blade assembly pushing against the movable die inserts. When the openings are decreased in widths, the stationary and movable halves of the openings grip the tubing on either side of where the blade cuts the tubing, enabling the tubing to be cut without deformation. Once the cut is completed, the cam means disengage the movable die inserts and die springs provided in pockets on the fixed die halves cause the openings to widen by pushing the movable die inserts away from the fixed die halves.
2. Prior Art
Small diameter welded seam tubing, such as that used in constructing radiators, must be cut to precise lengths. To reduce construction costs, a cutting mechanism must be able to cut the tubing quickly to the correct length without deforming the cut surfaces. Normally, the cutting mechanism travels along a moving strand of tubing stock while the tubing is being cut. Once finished cutting, the cutting mechanism quickly reverses direction of travel, moving backward the proper distance to engage the strand of tubing stock for another cutting cycle. Normally, a pair of cutting mechanisms work together to cut the tubing into tubes of a particular length, with one cutting mechanism cutting a first end of a tube and the other simultaneously cutting a second opposite end of the tube. Synchronization of these movements and the distance between the pair of cutting mechanisms is normally computer controlled to create tubes of the desired lengths.
Currently in the cutting process, tubing is inserted through openings in a pair of solid cut-off dies of the cutting mechanism and a blade moves between the dies to cut the tubing. One problem with using solid cut-off dies is that there must be a certain amount of clearance between the exterior tubing wall and the die openings in order for the tubing to move easily at high speed through the openings without binding. When the blade cuts the tubing, the clearance existing between the exterior tube wall and the die openings allows the tubing to move thus creating deformed, pear-shaped ends on the tubes rather than the desired flat, oval-shaped ends. Deformation of the ends of the tubes during the cut-off stroke renders the ends of the tubes unsuitable for use without further processing, which means that the tubes have to be increased in cut-off length at the tube mill to allow for further processing. The material needed for such an increased tube length and the additional processing required to correct the shape and size of the tube's cut ends adds to the cost of construction. Current die designs have no provision for adjusting the clearance between the dies and the tubing during the cut-off stroke, without sacrificing good high speed running clearance.
The present invention addresses this problem by replacing the solid cut-off dies with a pair of split dies that have movable die inserts. The movable die inserts, in conjunction with the fixed die halves, form split openings through which the tubing extends. The movable die inserts are capable of moving toward their associating fixed die halves to close on the tubing during the cut-off cycle in order to prevent the thin walled tubing from deforming as the cut-off blade enters the tubing and capable of then moving away from their associating fixed die halves to open to full clearance after cutting the tube. The movable die inserts are moved toward the fixed die halves during the cut-off cycle by engagement of cam tracks provided on the movable die inserts by cam rollers that are attached to a continuously rotating, spring loaded blade support arm. Once the cut-off cycle is complete, i.e. the blade support arm has rotated sufficiently for the attached blade to have passed through the tubing and for the cam rollers to have disengaged the movable die inserts, springs provided in the fixed die halves force the movable die inserts away from the fixed die halves, thus widening the openings to their full clearance positions through which the tubing may move easily at high speed.